The invention relates to plastic tube fluid handling means for use in heat exchangers and more particularly to such means with a metal barrier layer in the form of heat transfer ribbon.
Among the challenges in making plastic heat exchangers is the need for improved barrier properties. In some applications, such as air-air heat exchange, such as in a charge air cooler, permeability of the plastic tubes is not a problem. In other applications, permeability must be well managed. Among the highest demands for low permeability are refrigeration applications. There is a need to keep the refrigerant in and both water vapor or moisture and air out. Refrigerants are also under pressure, higher in condensers and lower in evaporators, adding to the need for good permeation control.
It has been recognized that metal layers will provide impermeability to polyamide tubes for use in heat exchangers. However, structures and procedures for obtaining good impermeability for practical use in refrigeration systems from the combination of metal and plastic or polyamide and aluminum are not available. Some have suggested applying metal after assembling a structure, such as by sputtering. However, sputtering, while it may give a complete coating, does not provide the impermeability needed. Also, thicker metal layers would be needed to permit improved heat transfer from a web to the tubes. Much of the art uses fins of aluminum brazed onto aluminum tubes perpendicular to the tubes to improve heat exchange, which is not readily done with plastic tubes.
Others have proposed a web between tubes, but no-one has yet developed an appropriate configuration of tubes and metal to obtain the needed impermeability, along with maximum heat transfer.
U.S. Pat. No. 4,069,811 discloses in FIG. 7 a heat exchanger element with spaced-apart copper or plastic tubes surrounded by and encased in spot-welded sheets of a rigid, preferably black, metal absorber plate. U.S. Pat. No. 5,469,915 shows tubes of plastic or metal encased in and held apart by plastic sheets. European Patent Publication 864,823 A2, discloses tubes for solar heat exchangers made of an elastomer or plastic inner layer, a stiffener layer of thermally conductive metal such as aluminum in the form of a mesh or a helical layer, and optionally an outer layer of the same elastomer or plastic. The inner polymer layer can be 0.1-2.5 mm (0.004-0.1 inches) thick, preferably 0.1-0.3 mm (0.004-0.012 inches), and the stiffener can be 0.1-2 mm (0.004-0.079 inches) thick. However, although the metal stiffener may absorb heat well, it is taught to be used as a mesh or helical layer, so it would not provide any degree of impermeability.
U.S. Pat. No. 3,648,768 shows making a web of plastic with parallel tubes spaced apart in the web. It says nothing about barrier layers or using metal in the webs.
The invention provides a structure for use in heat exchangers comprising a plurality of polymeric tubes arranged in parallel and placed at least 1xc2xd tube diameters apart measured center-to-center, said tubes being held in place by, surrounded by and sealed to a laminated foil, said foil having two faces, one facing toward the tubes, and the other facing away from the tubes, said foil comprising at least one layer of metal with at least one polymer layer on at least the side facing the tubes,
said tubes having an inner diameter in the range of 0.5-10 mm and a wall thickness in the range of 0.05-0.3 mm,
said foil having a total thickness in the range of 0.05-0.25 mm and a total metal thickness in the range of 0.002-0.1 mm.
Preferably, from 5 to 20 tubes are used in the structure, and preferably the inside diameter of the tubes is 1 to 3 mm (and most preferably having a wall thickness in the range of 0.1-0.25 mm). Moreover, preferably the total thickness of foil is in the range of 0.07-0.2 mm (most preferably 0.1-0.15 mm) and the total thickness of the metal layer(s) is preferably in the range of 0.005-0.02 mm (most preferably 0.005-0.01 mm).
Such a structure is herein referred to as a barrier ribbon. Reference is made throughout the case to xe2x80x9ctubesxe2x80x9d, xe2x80x9ctubingxe2x80x9d, and the like. It is to be understood that these terms are often used interchangeably, and it will be apparent to the reader that in some cases either term could apply.
Moreover, those having skill in the art to which the invention pertains will recognize that throughout the description the terms xe2x80x9cfoilxe2x80x9d, xe2x80x9claminated foilxe2x80x9d, xe2x80x9cfilmxe2x80x9d, and the like are intended to convey the same meaning.